SIP originated in late 1996 as a component of the IETF Mbone (Multicast backbone), an experimental multicast network on top of the public Internet. It was used by the IETF for the distribution of multimedia content, including IETF meetings, seminars and conferences. Because of its simplicity, power and extensibility, SIP was rapidly adopted for other uses across the IETF, most notably as a Voice Over Internet Protocol (VoIP) standard. Today, SIP is considered the emerging signaling standard for all IP communications with a real-time interactivity component such as VoIP, Instant Messaging, audio and video conferencing, e-learning, online gaming, etc.
SIP is used to establish, change and terminate sessions between one or more users in an IP-based network and is - as a part of the IETF standards process - modeled upon other Internet protocols such as SMTP and HTTP. SIP therefore brings a new degree of scalability, interoperability and ease-of-building new services lacking in earlier, more telecom-centric protocols such as H.323.
Using SIP, telephony becomes another web application and integrates easily into other Internet services. SIP is a simple toolkit that enterprises, application developers and service providers can use to build converged voice and multimedia services.